1. Field of the Invention
The present invention relates to a water-based ink. More specifically, the present invention relates to a water-based ink which is less likely to cause nozzle clogging, thereby imparting high print quality.
2. Discussion of the Related Art
In general, when characters are written with an ink on paper or printed with a printer, high quality is required for the characters.
Causation for lowering the print character quality includes feathering which is caused by spreading the ink along with fibers constituting paper, blotting, lowering of the drop directionality in an inkjet recording process, and the like.
For the purposes of reducing feathering and blotting, there has been proposed a water-based ink containing an alkylene oxide adduct having a relatively high molecular weight. However, there is a defect in the water-based ink such that the drop directionality is poor, thereby leading to a defect of lowered print character quality. The accuracy for expelling an ink droplet to a desired portion means that fine ink droplets are accurately expelled from a nozzle to a desired portion, that is, the surface of a recording medium.
In general, since an ink for inkjet recording is poor in water resistance and scratch and rub resistance, there has been proposed to use an aqueous dispersion of fine polymer particles containing a colorant to improve these properties. However, since the aqueous dispersion of fine polymer particles containing a colorant has film-forming property upon drying, there arise some defects such that dried substances are generated on the periphery of the nozzles, whereby the drop directionality is lowered.
In addition, in order to improve the drop directionality in generally used water-based ink as well as the water-based ink comprising an aqueous dispersion mentioned above, there have been proposed a water-based ink containing a surfactant having a long alkyl chain and a large number of moles of an alkylene oxide added, and showing a specific cloud point, such as polyethylene glycol lauryl ether (Japanese Patent Laid-Open No. Sho 60-32866); a water-based ink comprising a surfactant having a specific HLB value, such as polyoxyethylene nonylphenyl ether (Japanese Patent Laid-Open No. Hei 4-239067), and the like. Also, there has been proposed a water-based ink containing an additive such as polyalkylene oxide alkyl ether having a short alkyl chain and a small number of moles of an alkylene oxide added (Japanese Patent Laid-Open No. Sho 56-32566).
However, there are some defects in these water-based inks comprising an aqueous dispersion of fine polymer particles containing a colorant, such that the ink is spread along the fibers constituting paper to cause feathering or blotting when the surfactant or the additive is contained in an amount necessary for improving the drop directionality, so that print character quality is lowered, and print density is lowered, since surface tension of the ink is lowered.
An object of the present invention is to provide a water-based ink which is excellent in print density and print durability, has high print character quality, and is excellent in dry resistance and makes a water-fast print.
Another object of the present invention is to provide a water-based ink for inkjet recording which has excellent jetting stability and drop directionality.
These and other objects of the present invention will be apparent from the following description.
The present invention is directed to a water-based ink comprising an aqueous dispersion of fine polymer particles containing a colorant, and at least one polyalkylene oxide derivative selected from the group consisting of the compounds represented by the following formulae:
R1Oxe2x80x94(CH2CH2O)axe2x80x94Hxe2x80x83xe2x80x83(I)
Hxe2x80x94(OCH2CH2)bxe2x80x94Oxe2x80x94R2xe2x80x94Oxe2x80x94(CH2CH2O)cxe2x80x94Hxe2x80x83xe2x80x83(II)
R3Oxe2x80x94(CH2CH2O)dxe2x80x94(CH2CH(CH3)O)cxe2x80x94Hxe2x80x83xe2x80x83(III)
Hxe2x80x94(OCH2CH2)fxe2x80x94(OCH2CH(CH3))gxe2x80x94Oxe2x80x94R4xe2x80x94Oxe2x80x94(CH2CH(CH3)O)hxe2x80x94(CH2CH2O)ixe2x80x94Hxe2x80x83xe2x80x83(IV)
wherein each of a and d is independently a number of 10 to 40; each of b and c is independently a number of 5 to 20; e is a number of 1 to 3; f is a number of 5 to 20; each of g and h is independently a number of 0 to 4, wherein g+h is a number satisfying 1 to 4; i is a number of 5 to 20; each of R1 and R3 is independently a monovalent aliphatic group having 2 to 6 carbon atoms, a monovalent alicyclic group having 3 to 6 carbon atoms, or a monovalent aromatic group having 6 to 12 carbon atoms; R2 is a divalent aliphatic group having 3 to 6 carbon atoms, a divalent alicyclic group having 3 to 6 carbon atoms, or a divalent aromatic group having 6 to 12 carbon atoms; R4 is a divalent aliphatic group having 2 to 6 carbon atoms, a divalent alicyclic group having 3 to 6 carbon atoms, or a divalent aromatic group having 6 to 12 carbon atoms; and the oxyethylene chain and the oxypropylene chain in the formulae (III) and (IV) may be added in random or block forms.
Preferable aqueous dispersions of fine polymer particles containing a colorant include an aqueous dispersion of fine polymer particles containing a hydrophobic dye and an aqueous dispersion of fine polymer particles containing a pigment. Among them, the aqueous dispersion of fine polymer particles containing a pigment, especially an organic pigment or carbon black, is more preferable.
The polymer used in the aqueous dispersion of fine polymer particles containing a hydrophobic dye or pigment includes vinyl polymers, polyesters, polyurethanes, and the like. Among the polymers, the vinyl polymers are preferable.
A preferable vinyl polymer includes a polymer prepared by copolymerizing a monomer composition comprising (a) at least one vinyl monomer selected from the group consisting of acrylic acid esters, methacrylic acid esters and styrenic monomers; (b) a polymerizable unsaturated monomer having a salt-forming group; and (c) a monomer copolymerizable with the vinyl monomer and the polymerizable unsaturated monomer having a salt-forming group.
The vinyl monomer includes acrylic acid esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-amyl acrylate, n-hexyl acrylate, n-octyl acrylate and dodecyl acrylate; methacrylic acid esters such as methyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; and styrenic monomers such as styrene, vinyltoluene and 2-methylstyrene.
The unsaturated monomer having a salt-forming group includes cationic monomers having a salt-forming group and anionic monomers having a salt-forming group.
The cationic monomers having a salt-forming group include unsaturated tertiary amine-containing monomers, unsaturated ammonium salt-containing monomers, and the like. Among them, preferable examples include N,N-diethylaminoethyl acrylate, N-(Nxe2x80x2,Nxe2x80x2-dimethylaminoethyl) acrylamide, vinylpyridine, 2-methyl-5-vinylpyridine, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and the like.
The anionic monomers having a salt-forming group include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, unsaturated phosphoric acid monomers, and the like. Among them, preferable examples include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, and the like.
The monomer copolymerizable with the vinyl monomer and the polymerizable unsaturated monomer having a salt-forming group includes acrylamide monomers; methacrylamide monomers; hydroxyl group-containing monomers; macromers having a polymerizable functional group at one end such as silicone macromers, styrenic macromers, polyester macromers, polyurethane macromers, and poly(alkyl ether) macromers; and especially a macromer represented by the formula (V):
CH2xe2x95x90C(R5)COO(R6O)pR7xe2x80x83xe2x80x83(V)
wherein R5 is hydrogen atom or a lower alkyl group; R6 is a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero-atom; R7 is hydrogen atom or a monovalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero-atom; and p is a number of 1 to 60; and the like. These monomers can be used alone or in admixture of at least two kinds. These monomers are given by way of exemplification, without intending to limit the present invention to those exemplified ones.
Preferable hydroxyl group-containing monomers are 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate.
Preferable macromers represented by the formula (V) are polyethylene glycol(2 to 30) (meth)acrylate and methoxypolyethylene glycol(1 to 30) (meth)acrylate. The term xe2x80x9c(meth)acrylatexe2x80x9d employed in the present specification means acrylate or methacrylate.
Among these copolymerizable monomers, macromers are preferable, and the silicone macromer, the styrenic macromer and the poly(alkyl ether) macromer are more preferable.
It is desired that the content of the vinyl monomer in the monomer composition is 1 to 75% by weight, preferably 5 to 60% by weight, more preferably 10 to 50% by weight, from the viewpoints of improvement in dispersion stability of the polymer emulsion and heat stability, that is, avoidance of scorching on the inkjet printer head.
It is desired that the content of the polymerizable unsaturated monomer having a salt-forming group in the monomer composition is 2 to 40% by weight, preferably 5 to 20% by weight, from the viewpoints of improvement in dispersion stability of the polymer emulsion and avoidance of scorching on the inkjet printer head.
It is desired that the content of the monomer copolymerizable with the vinyl monomer and the polymerizable unsaturated monomer having a salt-forming group in the monomer composition is 5 to 90% by weight, preferably 10 to 85% by weight, more preferably 20 to 60% by weight, from the viewpoints of improvement in dispersion stability of the polymer emulsion and avoidance of scorching on the inkjet printer head.
In addition, it is preferable that the average particle diameter of the fine polymer particles (the average particle diameter being determined in accordance with the method described in Preparation Examples given below) is 20 to 200 nm, from the viewpoint of dispersion stability.
It is preferable that the weight-average molecular weight of the polymer (the weight-average molecular weight being determined in accordance with the method described in Preparation Examples given below) is 3000 to 50000, from the viewpoints of scorching of a printer head, durability of ink after printing, and facilitation of the dispersion.
The hydrophobic dye can be used without limitation to specified ones, as long as the hydrophobic dye can be contained in the fine polymer particles. Examples of the hydrophobic dye include oil dyes, disperse dyes, basic dyes, and the like. Among them, the oil dyes and the disperse dyes are preferable from the viewpoint of favorably containing the dyes in the fine polymer particles.
The oil dyes are not limited to specified ones. Examples of the oil dyes include C.I. Solvent Black 3, 7, 27, 29, 34; C.I. Solvent Yellow 14, 16, 29, 56, 82; C.I. Solvent Red 1, 3, 8, 18, 24, 27, 43, 51, 72, 73; C.I. Solvent Violet 3; C.I. Solvent Blue 2, 11, 70; C.I. Solvent Green 3, 7; C.I. Solvent Orange 2, and the like.
The disperse dyes are not limited to specified ones. Preferred examples include C.I Disperse Yellow 5, 42, 54, 64, 79, 82, 83, 93, 99, 100, 119, 122, 124, 126, 160, 184:1, 186, 198, 199, 204, 224, 237; C.I. Disperse Orange 13, 29, 31:1, 33, 49, 54, 55, 66, 73, 118, 119, 163; C.I. Disperse Red 54, 60, 72, 73, 86, 88, 91, 93, 111, 126, 127, 134, 135, 143, 145, 152, 153, 154, 159, 164, 167:1, 177, 181, 204, 206, 207, 221, 239, 240, 258, 277, 278, 283, 311, 323, 343, 348, 356, 362; C.I. Disperse Violet 33; C.I. Disperse Blue 56, 60, 73, 87, 113, 128, 143, 148, 154, 158, 165, 165:1, 165:2, 176, 183, 185, 197, 198, 201, 214, 224, 225, 257, 266, 267, 287, 354, 358, 365, 368; C.I. Disperse Green 6:1, 9, and the like.
It is desired that the hydrophobic dye is dissolved in an organic solvent in a concentration of at least 2 g/L, preferably 20 to 500 g/L, from the viewpoint of efficiently encapsulating the hydrophobic dye into the fine polymer particles.
The aqueous dispersion of the fine polymer particles containing the hydrophobic dye can be prepared by known emulsification process. For instance, the aqueous dispersion can be obtained by dissolving a polymer and a hydrophobic dye in an organic solvent, adding a neutralizing agent as occasion demands to ionize a salt-forming group in the polymer, adding water to the resulting mixture, thereafter emulsifying with an emulsifier as occasion demands, and distilling off the organic solvent.
As the pigment, any kinds of known inorganic pigment or organic pigments can be used. Also, an extender can be used together with the pigment, as occasion demands. The inorganic pigment includes carbon black, metal oxides, metal sulfides, metal chlorides, and the like. Among them, carbon black is preferable for a black water-based ink. The carbon black includes furnace black, lamp black, acetylene black, channel black, and the like. The organic pigment includes azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, quinophthalone pigments, and the like. The extender includes silica, calcium carbonate, talc, and the like.
As a process for preparing an aqueous dispersion of the fine polymer particles containing a pigment, it is preferable to employ a process comprising dissolving a polymer in an organic solvent; adding a pigment, water and a neutralizing agent, and a surfactant as occasion demands to the resulting solution; kneading the mixture to form a paste; thereafter diluting the resulting paste with water as occasion demands; and distilling off the organic solvent from the mixture to give an aqueous dispersion.
It is preferable that the amount of the hydrophobic dye or pigment in the fine polymer particles is 20 to 400 parts by weight, based on 100 parts by weight of solid content of the polymer, from the viewpoints of print density and facilitation of containing of the hydrophobic dye or pigment into the fine polymer particles. In addition, the content of the hydrophobic dye or pigment in the water-based ink is preferably 1 to 30% by weight, more preferably 3 to 15% by weight, from the viewpoints of print density and jetting stability.
The content of the fine polymer particles containing a colorant in the water-based ink is not limited to specified ones, as long as sufficient print density can be obtained. It is desired that the content of the fine polymer particles in the water-based ink is usually 2 to 35% by weight, preferably 4 to 20% by weight, more preferably 4 to 8% by weight, from the viewpoints imparting sufficient print density and dry resistance.
In the polyalkylene oxide derivatives represented by the formulae (I) to (IV), the compound represented by the formula (I) is preferable from the viewpoint of excelling in print durability, and the compound represented by the formula (II) is preferable from the viewpoint of excelling in dry resistance.
In the polyalkylene oxide derivatives represented by the formulae (II) and (IV), the oxyethylene chain (hereinafter abbreviated as xe2x80x9cEOxe2x80x9d) and the oxypropylene chain (hereinafter abbreviated as xe2x80x9cPOxe2x80x9d) may be added in random forms or in block forms. In addition, EO and/or PO may be added in divisions of at least two sites, or one of EO and PO may be arranged adjacently to R3, R4 or terminal hydrogen atom.
The polyalkylene oxide derivative represented by the formula (III) can be schematically represented by these abbreviations EO and PO. Its embodiments include R3Oxe2x80x94EOxe2x80x94POxe2x80x94H, R3Oxe2x80x94POxe2x80x94EOxe2x80x94H, R3Oxe2x80x94EOxe2x80x94POxe2x80x94EOxe2x80x94H, R3Oxe2x80x94POxe2x80x94EOxe2x80x94POxe2x80x94H, R3Oxe2x80x94EOxe2x80x94POxe2x80x94EOxe2x80x94POxe2x80x94H, R3Oxe2x80x94EOxe2x80x94POxe2x80x94EOxe2x80x94POxe2x80x94EOxe2x80x94H, and the like. Among them, R3Oxe2x80x94EOxe2x80x94POxe2x80x94EOxe2x80x94H is preferable. The PO may include xe2x80x94CH(CH3)CH2Oxe2x80x94 other than xe2x80x94CH2CH(CH3)Oxe2x80x94. The same can be said for the polyalkylene oxide derivative represented by the formula (IV).
In the polyalkylene oxide derivative represented by the formula (IV), it is preferable that the sum of g and h, i.e. g+h, is 2 to 4.
Concrete examples of R1 and R3 include monovalent aliphatic groups having 2 to 6 carbon atoms, such as ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, t-butyl group, hexyl group and isohexyl group; monovalent alicyclic groups having 3 to 6 carbon atoms, such as pyrrolidinyl group and cyclohexyl group; and monovalent aromatic groups having 6 to 12 carbon atoms, such as benzyl group and naphthyl group.
Concrete examples of R2 include divalent aliphatic groups having 3 to 6 carbon atoms, such as propylene group, isopropylene group, butylene group, isobutylene group and hexylene group. Preference is given to divalent aliphatic groups having 4 to 6 carbon atoms; divalent alicyclic groups having 3 to 6 carbon atoms, such as cyclohexylene group; and divalent aromatic groups having 6 to 12 carbon atoms, such as benzylidene group and naphthylene group, from the viewpoint of optimization of surface active ability.
In addition, concrete examples of R4 include divalent aliphatic groups having 2 to 6 carbon atoms, such as ethylene group, propylene group, isopropylene group, butylene group, isobutylene group and hexylene group. Preference is given to divalent aliphatic groups having 2 to 3 carbon atoms; divalent alicyclic groups having 3 to 6 carbon atoms, such as cyclohexylene group; and divalent aromatic groups having 6 to 12 carbon atoms, such as benzylidene group and naphthylene group, from the viewpoint of optimization of surface active ability.
The number-average molecular weight of the polyalkylene oxide derivative is preferably 500 to 2000, more preferably 700 to 1500, from the viewpoints of jetting stability, print quality and dry resistance.
The surface tension of the polyalkylene oxide derivative is preferably 50 mN/m or more at 25xc2x0 C. from the viewpoints of imparting excellent jetting stability and print quality, more preferably 55 to 65 mN/m at 25xc2x0 C. from the viewpoint of diminishing feathering and blotting of characters for a wide variety of recording media.
In addition, it is preferable that the surface tension of the polyalkylene oxide derivative is 50 to 62 mN/m at 25xc2x0 C., and 40 to 55 mN/m at 80xc2x0 C., from the viewpoint of improvement in drop directionality. Furthermore, in addition to the above conditions, it is more preferable that the difference between the surface tension of the polyalkylene oxide derivative at 25xc2x0 C. and the surface tension of the polyalkylene oxide derivative at 80xc2x0 C. is at least 5.5 mN/m.
The term xe2x80x9csurface tensionxe2x80x9d employed in the present specification refers to a value determined by using its 5 w/v % aqueous solution (the surface tension being determined by the method mentioned in the item [Surface Tension] given below).
In the present invention, since the chain length of the alkyl group of the polyalkylene oxide derivative is short and the number of the alkylene oxide added is large, the surface active ability is low, so that feathering and blotting are less likely to be generated.
It is desired that the content of the polyalkylene oxide derivative in the water-based ink is 1 to 15% by weight, preferably 4 to 10% by weight, from the viewpoints of imparting sufficient dry resistance and print durability to the resulting water-based ink.
It is preferable that a water-soluble organic solvent is contained in the water-based ink of the present invention. When the water-soluble organic solvent is contained, there is an advantage that the water-based ink is excellent in dry resistance.
The water-soluble organic solvent may be any one as long as its solubility against water is at least 1% by weight at 25xc2x0 C. Examples of the water-soluble organic solvent include polyhydric alcohols such as ethylene glycol, diethylene glycol, glycerol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, trimethylolpropane and trimethylolethane; nitrogen-containing cyclic compounds such as 2-pyrrolidone, xcex3-butyrolactam, urea and ethyleneurea; nitrogen-containing acyclic compounds such as acetamide and N-monomethylacetamide. These water-soluble organic solvents can be used alone or in admixture of at least two kinds. Among them, diethylene glycol, glycerol and 2-pyrrolidone are preferable.
The content of the water-soluble organic solvent in the water-based ink is not limited to specified ones, and it is preferable that the content is usually 5 to 30% by weight or so, from the viewpoint of dry resistance.
The water-based ink of the present invention may further contain an additive such as a surfactant, a pH adjusting agent or antiseptics, as occasion demands, within a range so as not to impair the object of the present invention.
The water-based ink of the present invention further contains water as balance so that each ingredient is contained in a desired amount.
The water-based ink of the present invention can be readily prepared by mixing desired amounts of an aqueous dispersion of fine polymer particles containing a colorant, a polyalkylene oxide derivative, a water-soluble organic solvent and water, and an additive as occasion demands.
Since the water-based ink of the present invention is excellent in jetting stability and drop directionality, the water-based ink can be suitably used as a water-based ink for inkjet recording.